1. Field of the Invention
The present invention relates to the exhaust gas recirculation system (EGR System) for an internal combustion engine and, more particularly, an exhaust gas recirculation valve (EGR Valve) for controlling the amount of exhaust gas recirculated through the exhaust gas recirculation system.
2. Description of the Prior Art
It is known to be effective for reducing the emission of nitrogen oxide (NOx) from internal combustion engines that a part of the exhaust gas is recirculated to the intake air. In order to obtain the optimum effect of the exhaust gas recirculation in view of the overall performance of an internal combustion engine, it is considered favorable that the ratio of the amount of exhaust gas recirculated to the total amount of exhaust gas, i.e., the exhaust gas recirculation ratio, is constantly maintained at a predetermined value. In order to accomplish a constant exhaust gas recirculation ratio, a region is provided in the route of the exhaust gas recirculation extending from the exhaust pipe of an engine to the intake tube thereof, said region being constantly maintained at atmospheric pressure, wherein a throttling means of a predetermined throttling ratio is provided at the entrance of said particular region. Several examples of an exhaust gas recirculation valve based upon the abovementioned principle so as to accomplish a constant exhaust gas recirculation ratio are disclosed, for example, in Japanese Patent Application 35241/72, U.S. Pat. No. 3,799,131 and U.S. Pat. No. 3,802,402. However these conventional exhaust gas recirculation valves have relatively complicated structures and, furthermore, since in these valves the exhaust gas flow is controlled by a conventional valve element-valve seat structure, there is a drawback in that the tight contact between the valve element and the valve seat is obstructed by small particles contained in the exhaust gas, thereby resulting in an inaccurate control of the exhaust gas flow. Furthermore, since the valve element is movably supported by a valve stem which in turn is slidably supported by a guide means, the small particles contained in the exhaust gas also enter into the space between the valve stem and the guide means thereby obstructing smooth operation of the valve element.